This invention relates to a process for producing films of ethylene-xcex1-olefin interpolymers having, in combination, the properties of improved surface haze, improved stiffness, and improved color. The process involves forming a film from a composition comprising an ethylene-xcex1-olefin interpolymer and an amount of from about 0.1% to less than 1% by weight, based on the composition, of a functionalized ethylene homopolymer or a functionalized ethylene-xcex1-olefin interpolymer.
Ethylene-xcex1-olefin interpolymer films are often employed in packaging and other applications where appearance is important. Usually in the case of packaging, it is desired that the film be optically transparent and glossy so that the product packaged within will be more attractive. Accordingly, it is desirable to provide a film that has not only improved surface haze properties, but also improved stiffness and color.
The novel process of the present invention for the production of ethylene-xcex1-olefin interpolymer films having improved surface haze, improved stiffness and improved color is comprised as follows. A composition comprising an ethylene-xcex1-olefin interpolymer and an amount of from about 0.1 to less than 1% by weight, based on the composition, of a functionalized ethylene homopolymer or a functionalized ethylene-xcex1-olefin interpolymer, as defined herein, is prepared. The composition is then formed into a film in any manner known in the art. In a preferred embodiment of the process, the film is formed utilizing the well-known blown film technique.
The novel process of the present invention for the production of ethylene-xcex1-olefin interpolymer films having improved surface haze, improved stiffness and improved color is comprised as follows. A composition comprising an ethylene-xcex1-olefin interpolymer and an amount of from about 0.1 to less than 1% by weight, based on the composition, of a functionalized ethylene homopolymer or a functionalized ethylene-xcex1-olefin interpolymer, as defined herein, is prepared. The composition is then formed into a film in any manner known in the art. In a preferred embodiment of the process, the film is formed utilizing the well-known blown film technique.
More particularly, the ethylene-xcex1-olefin interpolymer used in preparing the compositions, that are formed into the films of the present invention, is any ethylene-xcex1-olefin interpolymer comprising ethylene and at least one, or more, other xcex1-olefin wherein the ethylene content is at least about 50% by weight of the total monomers comprising the interpolymer. Preferably, the ethylene content of the interpolymer ranges from greater than about 50% to about 99% by weight of the total monomers comprising the interpolymer. The xcex1-olefin monomer(s) preferably contain from 3 to about 16 carbon atoms. Exemplary xcex1-olefins that may be utilized herein are propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 4-methyl-1-pentene, 1-decene, 1-dodecene, 1-hexadecene and the like. Also utilizable herein as the xcex1-olefin monomer are non-conjugated dienes and olefins formed in situ in the polymerization medium. The ethylene-xcex1-olefin interpolymers may be linear or may contain Theologically significant long chain branches, such as the xe2x80x9csubstantially linearxe2x80x9d polymers, and may be produced by any process, such as solution, gas phase, or slurry loop, and with any olefin polymerization catalyst, such as the constrained geometry, metallocene type, Ziegler Natta types, or chromium oxide types. The ethylene-xcex1-olefin interpolymer is present in the compositions utilized to form the films of the present invention, in an amount of from about greater than 99% to about 99.9% by weight of the composition.
The functionalized ethylene homopolymer or functionalized ethylene-xcex1-olefin interpolymer suitable for use herein are defined as follows. The polyethylene that is functionalized may be any homopolymer of ethylene. The interpolymer of ethylene that is functionalized and is suitable for use in preparing the compositions from which the films of the present invention are formed is any ethylene-xcex1-olefin interpolymer comprising ethylene and at least one, or more, other xcex1-olefin wherein the ethylene content is at least about 50% by weight of the total monomers comprising the interpolymer. Preferably, the ethylene content of the interpolymer ranges from greater than about 50% to about 99% by weight of the total monomers comprising the interpolymer. The xcex1-olefin monomer(s) preferably contain from 3 to about 16 carbon atoms. Exemplary xcex1-olefins that may be utilized herein are propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 4-methyl-1-pentene, 1-decene, 1-dodecene, 1-hexadecene and the like. Also utilizable herein as the xcex1-olefin monomer are non-conjugated dienes and olefins formed in situ in the polymerization medium. The ethylene-xcex1-olefin interpolymers may be linear or may contain Theologically significant long chain branches, such as the xe2x80x9csubstantially linearxe2x80x9d polymers, and may be produced by any process, such as solution, gas phase, or slurry loop, and with any olefin polymerization catalyst, such as the constrained geometry, metallocene types, Ziegler Natta types, or chromium oxide types.
In preparing the functionalized ethylene homopolymers or ethylene-xcex1-olefin interpolymers suitable for use herein, there may be utilized as the functionalizing agent any unsaturated monomer containing one or more carboxylic acid, carboxylic acid ester, or acid anhydride group. Examples of suitable functionalizing agents herein are carboxylic acids such as acrylic and methacrylic acid, carboxylic acid esters such as methyl acrylate and methyl methacrylate, and acid anhydrides such as maleic anhydride. Further exemplary functionalizing agents suitable for use herein are unsaturated monocarboxylic acids and polycarboxylic acids and cyclic acid anhydrides. Specifically included herein are acids such as maleic acid, fumaric acid, himic acid, itaconic acid, citraconic acid, mesaconic acid, acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, and acid anhydrides such as maleic anhydride and himic anhydride. Preferred for use herein as the functionalizing agent is maleic anhydride. Mixtures of functionalizing agents may be utilized in the present invention. The functionalizing agent is utilized in any amount that will functionalize the ethylene homopolymer and/or interpolymer such that the functionalized ethylene homopolymer and/or interpolymer will contain from about 0.01 to about 3% by weight of the at least one functionalizing agent, based on the functionalized ethylene homopolymer or copolymer. Preferably, the functionalizing agent will be utilized in an amount of from about 0.20 to about 10 weight percent, based on the weight of the ethylene component in order to produce the desired functionalized polymer.
The functionalized ethylene homopolymers and ethylene-xcex1-olefin interpolymers utilized herein may be prepared by any process known in the art. Exemplary of such processes for preparing functionalized ethylene homopolymers and copolymers are U.S. Pat. Nos. 4,612,155; 4,762,890; 5,180,788; 5,705,565; and 5,728,776; and International Publication No. WO 01/36495 A1.
The functionalized ethylene homopolymer or ethylene-xcex1-olefin interpolymer is present in the compositions utilized to form the films of the present invention, in an amount of from about 0.1 to less than 1% by weight of the composition.
The compositions, from which the novel films are formed, comprising from greater than 99 to about 99.9% by weight of the composition, of the ethylene-xcex1-olefin interpolymer described herein, and from about 0.1 to less than 1% by weight of the composition, of the functionalized ethylene homopolymer or functionalized ethylene-xcex1-olefin interpolymer described herein are prepared by any method known in the art. For example, the components of the composition may be admixed together on a conventional mixing machine such as a mill roll, an extruder or a continuous mixer. In preparing the compositions of the examples herein, pellets of the components were placed into a fiber drum and mixed for five minutes on an INS Plastic Tumbling unit. In more detail, in each of the following examples wherein a composition is prepared, the following procedure was utilized. A predetermined amount of ethylene-xcex1-olefin interpolymer and functionalized ethylene homopolymer or functionalized ethylene-xcex1-olefin interpolymer, both described herein, were weighed using a Toledo scale and placed into a fiber drum. The fiber drum was then placed on an INS Plastic Tumbling unit and mixed for a period of five minutes yielding the desired composition.
For many purposes, it may be desirable to incorporate other conventional additives with the compositions utilized in the present invention. For example, there may be added antioxidants, heat and light stabilizers, dyes, antistatic agents, lubricants, preservatives, processing aids, slip agents, antiblocking agents, pigments, flame retardants, blowing agents, and the like.
The compositions may be fabricated into films by any technique known in the art, and are particularly suitable for use with blown-film techniques. In further detail, the films of the examples were blown under the following conditions.
The tumbled pellet blends were fed to the hopper of a 2.5-inch (64-mm) Egan extruder, having a length to diameter ratio of 24/1 and a barrier screw. The extruder was equipped with a 6-inch (152-mm) diameter annular die having a die gap of 88 mil (2.2 mm). A dual-lip air ring was used for cooling the external surface of the tubular film as it exited the annular die. A xe2x80x9chump-backxe2x80x9d extruder temperature profile was employed with setpoints of 193, 232, 221, 216, and 204xc2x0 C. for zones 1 through 5, respectively, and a die setpoint of 218xc2x0 C. was employed. A throughput rate of 69 kg/h was maintained while producing films of 1-mil (0.025-mm) thickness with a blow-up ratio of 2.4. A frost line height of 38 cm was maintained during the film formation. Films were wound into rolls of about 60 linear meters and aged for 40 hours at standard lab conditions (23xc2x0 C. and 50% relative humidity) before testing.
The invention will be more readily understood by reference to the following examples. There are, of course, many other forms of this invention which will become obvious to one skilled in the art, once the invention has been fully disclosed, and it will accordingly be recognized that these examples are given for the purpose of illustration only, and are not to be construed as limiting the scope of this invention in any way. Moreover, all U.S. patents referred to herein are incorporated by reference in their entirety.